Each year, more than 5 million seriously ill patients are admitted to ICUs in the United States. Rates of depression following discharge are far greater for these patients than for the general population, according to the study.

"It's very clear that ICU survivors have physical, cognitive and psychological problems that greatly impair their reintegration into society, return to work and being able to take on previous roles in life," said study senior author Dr. Dale Needham, professor of medicine at Johns Hopkins University School of Medicine in Baltimore.

"If patients are talking about the ICU being stressful, or they're having unusual memories or feeling down in the dumps, we should take that seriously," Needham said in a university news release.

"Health care providers, family members and caregivers should pay attention to those symptoms and make sure they're not glossed over," Needham added.

The Johns Hopkins researchers reviewed 42 studies that included more than 4,000 former ICU patients in the United States and United Kingdom.

Two to three months after being discharged from the ICU, 29 percent of patients had at least mild depression. Six months after discharge, rates of mild depression were 34 percent. One year after discharge, 29 percent of former ICU patients were mildly depressed, the researchers found.

Moderate to severe depression was present in 17 percent of patients two to three months after discharge, and persisted six months after discharge. By 12 to 14 months, the rate of moderate to severe depression dropped slightly, to 13 percent.

The rates of depression among former ICU patients are three to four times higher than in the general population, according to study co-author Dr. O. Joseph Bienvenu. He's an associate professor of psychiatry and behavioral sciences at the school of medicine.

The risk of depression was highest among patients who had psychological symptoms before their ICU stay and among those who had psychological distress symptoms while in the ICU or hospital. These symptoms include anger, nervousness and acute stress symptoms, such as emotional detachment or flashbacks.

"Not only can people with depression have slower physical recovery, but they also experience financial strain because they often cannot return to work and their caregivers must stay home with them," Bienvenu said.

The study appears in the September issue of the journal Critical Care Medicine.